UNITED NATIONS, April 3 (Reuters) - Syria has packed 40 percent of its chemical weapons arsenal into containers to be taken outside the country and destroyed, and convoy security has been deployed to deal with violence around the port city of Latakia, the head of the mission overseeing the operation said on Thursday.

Syria's U.N. envoy warned that the government may be forced to delay its transports due to the security situation and might miss another deadline for moving the ingredients of its poison gas program out of the country.

Sigrid Kaag, head of the joint mission of the United Nations and the Organization for the Prohibition of Chemical Weapons, told the U.N. Security Council the toxins had been loaded into 72 containers at three different sites, said council diplomats who attended the meeting, speaking on condition of anonymity.

Once those 72 containers are shipped out of war-torn Syria, some 90 percent of the country's declared chemical weapons stockpile will have been removed for destruction, Kaag told a closed-door council briefing via video link from Damascus.

The United Nations said on Thursday that since March 20, no chemicals had been transported to Latakia, where they are to be shipped out of the country for destruction. So far almost 54 percent of Syria's declared chemicals have been removed.

Kaag told the Security Council that the Syrian authorities had assigned forces to provide security for the convoys to deal with the increased violence in the Latakia area, diplomats said.

Islamist insurgents launched an offensive around March 20 into Syria's Latakia region on the Mediterranean coast, taking both the border crossing with Turkey and the Armenian Christian village of Kasab on the Syrian side.

Syrian President Bashar al-Assad has sent army and militia reinforcements, backed by air power, to repulse the rebels, leading to heavy fighting across the strip of territory along the Turkish border. Turkey has fired back into Syria in retaliation for shells landing in its territory.

"Syrian authorities informed the joint mission that in view of the deteriorating security situation in Latakia province it would be temporarily postponing scheduled movements of chemical materials," U.N. spokesman Farhan Haq told reporters.

"The joint mission has impressed upon the Syrian authorities the need to resume movements as soon as possible in order to meet the timelines for the complete removal and destruction of Syria's chemical weapons program," he said.

DEADLINE AT RISK

Kaag told the council the Syrian authorities said on Sunday they wanted to resume transporting chemicals to Latakia "in coming days" and that if operations restarted immediately then the deadlines could still be met to remove all the chemicals from Syria by the end of April and destroying them by June 30.

However, she added that the timeline was becoming increasingly challenging, the diplomats said.

Assad agreed to destroy his chemical weapons following global outrage over a sarin gas attack in Ghouta in August that killed hundreds. The gas attack sparked a U.S. threat of military strikes, which was dropped after Assad agreed to give up his chemical arms.

The Syrian government, locked in a three-year-old war with rebels seeking to overthrow Assad, failed to meet a Feb. 5 deadline to move all of its declared chemical substances and precursors, some 1,300 tonnes, out of the country. It has since agreed to the new April 30 deadline.

"The deadline set up by the Syria government and Mrs Kaag and the OPCW will not be possible to be respected fully unless the security situation evolves in the right direction," Syrian U.N. Ambassador Bashar Ja'afari told reporters on Thursday.

He said some of the 15 Security Council members had blocked a Russian proposal to issue a statement expressing "the serious warning by the council of the consequences of these terrorist attacks on the port of Latakia against the shipments of the chemical materials."

Nigeria's U.N. Ambassador Joy Ogwu, president of the council for April, said council members were still negotiating a statement on the issue. "The security concerns in Syria were acknowledged by all of us," she said of the comments made by members during Kaag's briefing.

Russia, supported by China, has shielded its ally Syria on the Security Council during the civil war. They had previously vetoed three resolutions that would have condemned Syria's government and threatened it with possible sanctions.

Syria's civil war has killed more than 150,000 people, a third of them civilians, and caused millions to flee. The Syrian government and the opposition have accused each other of using chemical weapons during the conflict, and both have denied it. (Reporting by Michelle Nichols; Editing by Mohammad Zargham)

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